JP2012080963A - X-ray image photographing method and x-ray image photographing apparatus - Google Patents

Abstract

An X-ray imaging method capable of imaging a high-resolution phase contrast image and a high-resolution absorption contrast image in a short time according to the purpose only by finely adjusting a distance between a sample and a detector with respect to an X-ray source. And an X-ray imaging apparatus.
An X-ray imaging method that enables imaging of a fine structure with high spatial resolution using an X-ray source having a finite size, wherein the distance from the X-ray source 110 to a sample 500 is L, When the distance from the sample 500 to the detector 130 is d, d / L is sufficiently smaller than 1. When the average wavelength of X-rays emitted from the X-ray source 110 is λ and the resolution of the detector 130 is Δ, the distance between the peak position and the valley position of the phase contrast is 1 / 3Δ or more and 3Δ or less. It is.
[Selection] Figure 1

Description

  The present invention relates to an X-ray image capturing method and an X-ray image capturing apparatus that use an X-ray source having a finite size and can capture a fine structure.

  Conventionally, in the field of X-ray transmission imaging, the resolution of the detector is at most a dozen μm. Therefore, in order to capture an image with high resolution, an X-ray source having a focal point size as small as 10 μm or less is used, and the sample is enlarged and projected to capture an image. That is, the distance from the X-ray source to the sample is reduced, the distance from the sample to the detector is sufficiently large, and the distance is adjusted to adjust the magnification.

  On the other hand, methods for performing imaging using phase contrast and imaging using absorption contrast with the same apparatus have been studied (Patent Documents 1 to 3, Non-Patent Document 1). For example, Patent Document 1 discloses a method of capturing an image in which an edge is emphasized using a phase contrast with a ratio of a distance from a sample to a detector and a distance from an X-ray source to a sample being 0.5. ing.

Japanese Patent Laid-Open No. 2001-238871 JP 2006-26425 A International Publication No. 2007/007473 Pamphlet

Hiroshi Ohara, Satoshi Yoshitomo, Satoshi Ishizaka, Tsuyoshi Honda, “Principles and Images of Phase Contrast Mammography”, Vol.23 (2006), No.2, pp.27-33

  However, in the X-ray transmission image capturing method using the enlarged projection as described above, the enlargement magnification is determined by the arrangement of the X-ray source, the sample, and the detector. Therefore, under high magnification photographing conditions for photographing a fine structure with high resolution, it is not easy to freely adjust the ratio between the phase contrast and the absorption contrast while maintaining the magnification. On the other hand, a method using an electron beam such as SEM or TEM can obtain a high-resolution image of a sample surface or a thin sample, but it is difficult to photograph the structure inside a thick sample.

  The present invention has been made in view of such circumstances, and by finely adjusting the distance between the sample and the detector with respect to the X-ray source, a high-resolution phase contrast image and a high-resolution absorption contrast image can be obtained depending on the purpose. An object of the present invention is to provide an X-ray image capturing method and an X-ray image capturing apparatus capable of capturing an image in a short time.

(1) In order to achieve the above object, an X-ray imaging method according to the present invention uses an X-ray source having a finite size and enables X-ray imaging to enable imaging of a fine structure with high spatial resolution. In this method, when the distance from the X-ray source to the sample is L and the distance from the sample to the detector is d, d / L is sufficiently smaller than 1, and the X-ray irradiated from the X-ray source Where λ is the wavelength of λ and the resolution of the detector is Δ, the following formula is satisfied.
In a normal X-ray source, the emitted X-ray includes not only one wavelength λ but also a number of X-ray wavelengths. In such a case, λ in Equation 1 is replaced with a numerical value obtained by weighted averaging according to the spectrum irradiated on the sample.

  Due to the above features, a phase contrast image in which the contour of the sample is emphasized on the order of microns can be taken by simply adjusting the arrangement of the sample and the detector with respect to the X-ray source in the range of d / L << 1, and CT reconstruction by absorption contrast can be performed. Make it possible to configure. In addition, a high-power X-ray source having a relatively large focal spot size can be used, and a high-resolution X-ray transmission image can be obtained in a short time. Note that being sufficiently smaller than 1 means that the photographing magnification described by (L + d) / L = 1 + d / L is approximated by 1.

  (2) Further, the X-ray imaging method according to the present invention is characterized in that the d / L is 0.1 or less. As a result, even if a high-power X-ray source having a sufficiently large focal size is used, not only an image can be obtained with a resolution of several microns or less using a high-resolution detector, but also the focal position drift of the X-ray source can be prevented. Stable shooting can be performed.

  (3) Further, the X-ray imaging method according to the present invention is characterized in that a focal spot size of the X-ray source is sufficiently larger than the Δ. This makes it possible to use a high-power X-ray source without being limited by the focal spot size. Note that sufficiently large means that it is large enough to satisfy, for example, S> 10Δ.

  (4) The X-ray imaging method according to the present invention is characterized in that the detector has a spatial resolution of 2 μm or less. Thereby, an X-ray transmission image can be detected with high resolution.

  (5) Further, the X-ray imaging method according to the present invention is characterized in that the power supplied when the X-ray source is used is 30 W or more. Thereby, it can image | photograph in a short time using big electric power.

  (6) Further, the X-ray imaging method according to the present invention is characterized in that a minute focal point formed by converging divergent X-rays with an X-ray optical element is used as a virtual light source for the X-ray source. Yes. As a result, if a single color virtual light source is used, it is possible to photograph with one λ. In addition, the absorption coefficient can be calculated quantitatively, and CT reconstruction with quantitative density information becomes possible.

  (7) Further, an X-ray imaging apparatus according to the present invention has a finite size, an X-ray source that generates X-rays, a support base that supports a sample irradiated with the generated X-rays, A detector that detects X-rays transmitted through the sample, and when the distance from the X-ray source to the sample is L and the distance from the sample to the detector is d, the X-ray source, The arrangement of the support base and the detector is adjusted so that d / L is sufficiently smaller than 1 so that the fine structure of the sample can be photographed.

  As a result, by adjusting the arrangement of the sample and detector with respect to the X-ray source, it is possible to take an image with a phase contrast that emphasizes the contour of the sample, or to select and take an image with an absorption contrast freely. Enables CT reconstruction with high performance and low artifacts. Further, by using a powerful X-ray source, a high-resolution X-ray transmission image can be obtained in a short time.

  According to the present invention, by finely adjusting the arrangement of the sample and the detector with respect to the X-ray source, a phase contrast image and an absorption contrast image can be taken in a short time and with high resolution.

It is the schematic which shows the configuration for the X-ray image imaging method which concerns on this invention. It is a figure which shows the relationship between a focus and projection. It is a figure which shows the distance between the peak position and trough position of a phase contrast. (A) (b) The relationship between the distance f between the peak and trough of the intensity and the distance d between the sample and the detector when phase contrast is generated by plane waves with a sample size of 10 μm and a sample size of 50 μm, respectively. It is a graph which shows a simulation result. (A) (b) It is a graph which shows the simulation result about the relationship of the distance of the intensity | strength peak and trough, and the wavelength (lambda) of X-ray when a phase contrast is produced by a plane wave, respectively by sample size 10micrometer and sample size 50micrometer. . (A), (b) It is the X-ray transmission image of the plant cell image | photographed when the distance of a sample and a detector is 1 mm and 5 mm, respectively. (A), (b), (c) is a CT image of two orthogonal cross sections and an enlarged cross section of a carbon fiber reinforcement plastic (CFRP, carbon fiber reinforced resin), respectively. (A), (b) It is CT image of the cross section which cut | disconnected the leg of the ant | vertical vertically, and the cross section of the direction along a leg | foot, respectively. It is a figure which shows the configuration which produces | generates the virtual light source which concerns on 2nd Embodiment.

  Next, embodiments of the present invention will be described with reference to the drawings. In order to facilitate understanding of the description, the same reference numerals are given to the same components in the respective drawings, and duplicate descriptions are omitted.

[First Embodiment]
(Device configuration)
FIG. 1 is a schematic diagram showing a configuration for an X-ray imaging method of the present invention. Such a configuration is configured by the arrangement of each part of the X-ray imaging apparatus 100. As shown in FIG. 1, the X-ray imaging apparatus 100 includes an X-ray source 110, a support 120, and a detector 130.

  The X-ray source 110 is an X-ray source used in a laboratory having a finite focal size. The X-ray source 110 does not use synchrotron radiation. Specifically, an X-ray source targeting copper, molybdenum, tungsten or the like is used, and the type is not particularly limited, but the arrangement of each part is adjusted according to the wavelength of the characteristic X-ray. The X-ray source 110 is not necessarily limited to the electron collision type, plasma X-ray, inverse Compton radiation, and includes a virtual light source described later.

  The focal spot size of the X-ray source 110 is preferably sufficiently larger than the resolution Δ of the detector. Thus, the high-power X-ray source 110 can be used without being limited by the focal spot size. Since d / L is sufficiently smaller than 1, stable imaging can be performed even with respect to the drift of the focal position of the X-ray source 110. Note that the power supplied to the X-ray source 110 is preferably 30 W or more, and more preferably 100 W or more. By supplying such a large electric power, an X-ray image can be taken in a short time.

  The support table 120 supports the sample 500 irradiated with X-rays. The support table 120 can fix the sample 500 and can be rotated. It is preferable that the rotational shaft is less shaken, and it is particularly preferable that this be 1 μm or less. Thereby, high-resolution CT reconstruction can be realized without correction by software.

  The detector 130 detects X-rays that have passed through the sample 500. The detector 130 has a high spatial resolution of less than 10 μm. The spatial resolution of the detector 130 is preferably 7 μm or less, and more preferably 1 μm or less. As a result, high-resolution detection can be performed using a high-resolution X-ray transmission image. The X-ray imaging apparatus 100 using a monochromatic X-ray using a virtual light source can obtain a high-contrast image even for a delicate sample, which is a fine tissue such as a soft tissue of a living body or an organic industrial product. It is suitable for observing simple structures.

  The X-ray imaging apparatus 100 has, for example, a slide mechanism (not shown), and can be finely adjusted by controlling the arrangement of the support 120 or the detector 130 with respect to the X-ray source 110. Then, it is possible to capture an image in which the contour by phase contrast is emphasized by fine adjustment within the range of d / L << 1, and an image suitable for CT reconstruction by absorption contrast. At this time, since d / Δ << 1, the magnification (L + d) / L = 1 + d / L is about 1, and the degree of phase contrast can be adjusted without changing the magnification and the field of view.

(Image shooting)
An image can be captured using the X-ray image capturing apparatus 100 configured as described above. When the distance from the X-ray source 110 to the sample 500 is L and the distance from the sample 500 to the detector 130 is d, the arrangement of the X-ray source 110, the support 120 and the detector 130 is adjusted, and d / L is Measurement is made sufficiently smaller than 1. d / L is preferably 0.1 or less. In this way, the fine structure of the sample 500 can be photographed.

  FIG. 2 is a diagram illustrating the relationship between the focal point and the projection. In the arrangement as described above, d / L is small, and the focal point size S of the X-ray source is projected to be reduced by d / L times on the detector 130. Therefore, the size of the image of the X-ray source projected on the detector 130 is large. The depth δ is reduced by d / L times. Therefore, not only a high-resolution image can be taken even if an X-ray source having a sufficiently large focal point size is used, but also the influence of the drift of the focal point position can be suppressed. As a result of using such a high-power X-ray source having a large focal spot size, efficient imaging can be performed in a short time.

The arrangement of each part of the X-ray imaging apparatus 100 satisfies the following conditions in addition to sufficiently reducing d / L. That is, when the average wavelength of X-rays emitted from the X-ray source 110 is λ and the resolution of the detector 130 is Δ, the configuration of the X-ray imaging apparatus 100 satisfies the following mathematical formula.

  By adjusting the distance d from the sample 500 to the detector 130 within the range of the above formula (1), the arrangement of the sample 500 and the detector 130 with respect to the X-ray source 110 is adjusted, and the contour of the sample is emphasized by phase contrast. It is possible to take an image or to take an image for CT reconstruction with absorption contrast.

X-rays spread due to refraction and show a shadow. The projected intensity distribution shape is determined by the distance d between the position of the sample 500 and the detector 130. The X-ray imaging apparatus 100 can adjust this distance d to an appropriate size. FIG. 3 is a diagram illustrating the distance between the peak position and the valley position of the phase contrast. The distance f (λ, d) between the peak position and the valley position of the phase contrast is a so-called phase contrast (phase fringe), and can be derived as follows by considering Fresnel diffraction.

  4 (a) and 4 (b) show the distance f between the peak and trough of the intensity when a phase contrast is generated by a plane wave for a cylindrical sample having a diameter of 10 μm and a diameter of 50 μm, and the sample and detector. It is a graph which shows the simulation result of the relationship with the distance d between. At this time, the wavelength λ of the X-ray is calculated as 229 pm. As shown in FIGS. 4A and 4B, the distance f is about 1 μm when d = 5 mm regardless of the diameter of the sample. 5 (a) and 5 (b) show the peak-to-valley distance f and X-ray wavelength λ when phase contrast is generated by plane waves on cylindrical samples having diameters of 10 μm and 50 μm, respectively. It is a graph which shows the simulation result about this relationship. At this time, the distance d from the sample 500 to the detector 130 is 2 mm. As shown in FIGS. 5A and 5B, regardless of the diameter of the sample, for example, at a wavelength of 229 pm, the distance f is about 0.65 μm. The above formula (2) is obtained by formulating these relationships.

  If f given in this way is about the resolution of the detector 130 or higher, the contour of the captured image can be enhanced. However, the image in which the edge is emphasized in this way has a difference in intensity more than the actual difference in absorption coefficient, and is not suitable for quantitative evaluation of the absorption coefficient. For example, when an X-ray image is used for CT reconstruction, since the edge is excessively emphasized from any direction, strong artifacts are generated and reconstruction is difficult.

  Therefore, for CT reconstruction, the phase contrast is suppressed and an image with absorption contrast is taken. In this case, it is preferable to finely adjust the phase contrast f (λ, d) so that the value is smaller than the value of the resolution Δ of the detector 130 for imaging. Therefore, in a scene where an image with absorption contrast is taken, it is only necessary that the phase contrast f (λ, d) satisfy at least a range in which the resolution Δ of the detector 130 is not less than 1/3 and not more than 1 time. The X-ray imaging apparatus 100 needs to be able to finely adjust the arrangement of each part at least within the range.

  On the other hand, when a transmission image is captured with the edge emphasized, it is necessary to adjust so that the resolution Δ of the detector is smaller than the value of the phase contrast f (λ, d). Therefore, at the time of photographing, the arrangement of each part is adjusted within a range in which the phase contrast f (λ, d) is not less than 1/3 and not more than 3 times the resolution Δ of the detector 130 as shown in Equation (1). Thus, both the phase contrast image and the absorption contrast image can be taken by observing the fine structure.

Example 1
Next, an experiment using the X-ray imaging apparatus 100 will be described. First, an X-ray transmission image using phase contrast was taken using a plant leaf as a sample. A detector 130 having a supply power of 875 W, a Cr target, an X-ray source 110 with a focal size of 70 μm, and a pixel size of 0.65 μm (spatial resolution of 0.65 μm) was used. The distance L between the X-ray source 110 and the sample 500 was 250 mm. 6A shows a plant photographed when the distance d between the sample 500 and the detector 130 is 1 mm, and FIG. 6B shows a plant photographed when the distance d between the sample 500 and the detector 130 is 5 mm. It is a figure which shows the X-ray-transmission image of the cell.

  As shown in FIG. 6 (a), when the distance d was 1 mm, an X-ray transmission image with an absorption contrast in which the edge of the cell wall was not emphasized was obtained. At this time, f (λ, d) is 0.5 μm, which is smaller than the detector resolution Δ = 0.65 μm. In addition, as shown in FIG. 6B, when the distance d was set to 5 mm, an X-ray transmission image in which the edge of the cell wall was emphasized was obtained. At this time, f (λ, d) is 1.1 μm, which is larger than the resolution Δ = 0.65 μm of the detector. In this way, an X-ray image is taken in an arrangement in which d / L is sufficiently smaller than 1 and f (λ, d) satisfies the above formula (1), and the phase contrast is clear on the micron order. I was able to get an image.

(Example 2)
Under the same conditions as in the above examples, an X-ray transmission image using absorption contrast was taken using a carbon fiber reinforcement plastic (CFRP, carbon fiber reinforced resin) as a sample, and three-dimensional CT reconstruction was performed. The distance L between the X-ray source 110 and the sample 500 is 250 mm, and the distance d between the sample 500 and the detector 130 is arranged at 2 to 3 mm, which is between the above two examples, and the phase contrast is not overemphasized. Adjusted so that it was shot.

  FIGS. 7A, 7B, and 7C are CT images of two orthogonal cross sections and an enlarged cross section of a carbon fiber reinforcement plastic (CFRP, carbon fiber reinforced resin), respectively. Carbon fibers have high strength in the fiber direction, but the strength in other directions is not sufficient, and therefore fibers in many directions are stacked in multiple layers. As shown in FIG. 7, carbon fibers stacked in different directions, plastics connecting them, and gaps between them could be clearly distinguished and observed. Note that the large crack-shaped gap is generated by breaking the bond at the interface.

(Example 3)
Further, under the same conditions as in the above example, an X-ray transmission image using absorption contrast was taken using the joint portion of the ant's foot as a sample, and three-dimensional CT reconstruction was performed. The distance L between the X-ray source 110 and the sample 500 was 250 mm, and the distance d between the sample 500 and the detector 130 was adjusted to 2 to 3 mm. FIGS. 8A and 8B are CT images of a cross section obtained by vertically cutting an ant's foot and a cross section in a direction along the foot, respectively. As shown in FIGS. 8 (a) and 8 (b), it was observed that there was a liquid and muscle fibers wrapped in it inside the exoskeleton of the foot. In this way, an X-ray image was taken at a d / L of about 0.008 to 0.012 which is sufficiently smaller than 1, and a clear CT image on the micron order could be obtained. As described above, it was proved that an X-ray microscope having a resolution of micron order can be realized.

[Second Embodiment]
In the X-ray source 110, a minute focus formed by converging divergent X-rays with an X-ray optical element can be used as a virtual light source. FIG. 9 is a diagram showing a configuration for generating a virtual light source as the X-ray source 110. As shown in FIG. 9, the configuration for generating a virtual light source is composed of an actual X-ray source 210 that emits divergent X-rays, a first mirror 220, and a second mirror 230 (X-ray optical element). As a result, the X-ray source 110 of the virtual light source can be generated.

  The virtual light source size obtained in this way is preferably 100 μm or less. The virtual light source size is more preferably 50 μm or less or 20 μm or less. When the virtual light source size is 10 μm to several tens of μm, the effect is great in obtaining an X-ray image having a resolution of about 1 μm. A virtual light source can be shaped using a pinhole or slit to obtain a light source of an appropriate size.

  As shown in FIG. 9, the first mirror 220 reflects X-rays generated by the actual X-ray source 210 in a plane parallel to the support table 120, and the second mirror 230 is the first mirror. The X-ray reflected by 220 is reflected in a plane perpendicular to the support table 120.

  As the first mirror 220 and the second mirror 230, for example, a multilayer film mirror (multilayer film optical element) can be used. Thereby, only the X-rays having the wavelength of the characteristic line (CuKα) can be selectively extracted with respect to the condensing by the first mirror 220 and the condensing by the second mirror. Further, since the lattice constant can be changed depending on the incident position of the X-ray, diffraction can be caused by adjusting the lattice constant even when the incident angle changes.

  The first mirror 220 and the second mirror 230 may be formed of a crystal plate (crystal optical element). Thereby, for example, the first or second mirror can take out only the X-ray of Kα1. Alternatively, the first mirror 220 and the second mirror 230 may be configured by total reflection mirrors to limit the wavelength of the reflected X-rays to a long wavelength.

  Thus, by using a monochromatic virtual light source obtained by a multilayer mirror or a crystal plate, it is possible to photograph with one λ. As a result, the absorption coefficient can also be calculated quantitatively, CT reconstruction with quantitative density information is facilitated, and quantitative concentration mapping is also possible. In addition, by using a virtual light source, the focal spot size can be reduced, while sufficient power can be maintained to generate X-rays.

100 X-ray imaging apparatus 110 X-ray source (including virtual light source)
120 Support stand 130 Detector 210 X-ray source (real X-ray source)
220 First mirror (first X-ray optical element)
230 Second mirror (second X-ray optical element)
500 Sample L Distance from X-ray source to sample d Distance from sample to detector f Phase contrast (distance between peak position and valley position)
S Focus size of X-ray source δ Projected image size Δ Detector resolution

Claims (7)

An X-ray imaging method that enables imaging of a fine structure with high spatial resolution using an X-ray source having a finite size,
When the distance from the X-ray source to the sample is L and the distance from the sample to the detector is d, d / L is sufficiently smaller than 1,
An X-ray imaging method characterized by satisfying the following formula, where λ is the wavelength of X-rays emitted from the X-ray source, and Δ is the resolution of the detector.
  2. The X-ray imaging method according to claim 1, wherein the d / L is 0.1 or less.   The X-ray imaging method according to claim 1, wherein a focal spot size of the X-ray source is sufficiently larger than the Δ.   The X-ray imaging method according to claim 1, wherein the detector has a spatial resolution of 2 μm or less.   The X-ray imaging method according to any one of claims 1 to 4, wherein the power supplied when the X-ray source is used is 30 W or more.   6. The X-ray source according to claim 1, wherein a minute focal point formed by converging divergent X-rays with an X-ray optical element is used as the virtual light source. Line image shooting method. An X-ray source having a finite size and generating X-rays;
A support for supporting the sample irradiated with the generated X-ray;
A detector for detecting X-rays transmitted through the sample,
When the distance from the X-ray source to the sample is L and the distance from the sample to the detector is d, the arrangement of the X-ray source, the support base and the detector is adjusted. An X-ray imaging apparatus characterized by being sufficiently small so that the fine structure of the sample can be imaged.